TARGETING (betaARK1 IN HEART FAILURE: Heart failure (HF) is a major health problem and effective therapies have been elusive. Elucidating specific mechanisms involved in the pathogenesis of HF may identify novel molecular targets for treatment. A body of evidence is growing demonstrating that the actions of G protein-coupled receptor kinases (GRKs), such as the (beta-adrenergic receptor kinase (betaARK1 or GRK2), are important in modulating normal and failing heart function. Manipulation of betaARK1 expression and/or GRK activity in the hearts of transgenic mice has led to profound cardiac effects including enhanced function when a peptide inhibitor of (betaARK1 (betaARKct) is expressed. Global betaARK1 gene ablation led to embryonic lethality, however heterozygous knockout animals with 50 percent less (betaARK1 had enhanced cardiac function like betaARKct mice. The (betaARKct is the carboxyl terminal domain of betaARK1 and blocks the binding of betaARK1 to the bg subunits (Gbetagamma) of G proteins, a process required for activation of this GRK. Cardiac betaARKct expression has also "rescued" several mouse models of HF. Therefore, our Central Hypothesis is that betaARK1 plays a critical role in the pathogenesis of HF and inhibiting this GRK represents a novel therapeutic strategy. However, specific mechanistic insight into the actions of betaARK1 is clouded by the fact that the betaARKct targets Gbetagamma, which may have critical non-GRK functions. Moreover, non-betaARKct regions of betaARK1 (i.e. the amino terminus) may play a novel role in GRK actions. In this proposal, we will utilize novel molecular reagents and genetic techniques in mice to investigate the mechanistic role of (betaARK1, Gbetagamma and the (betaARKct in the normal and failing heart. Specific Aims are: (1) To determine the ultimate role of (betaARK1 in myocardium by investigating the functional impact of the loss of this GRK in the normal and failing heart using conditional and tissue-specific knockout mice. (2) To specifically investigate the role of Gbetagamma in the heart by studying transgenic mice with expression of a distinct non-betaARK1 Gbetagamma-binding domain. (3) To determine novel in vivo cardiac roles of betaARK1 by targeted expression of the amino-terminal domain of this kinase in mice. (4) To determine the ventricular gene expression changes induced by these above genetic manipulations in HF models and to evaluate genomic changes with those previously associated with the betaARKct phenotype.